From Joining to Leaving: Domestic Law's Role in the International Legal Validity of Treaty Withdrawal

If a state withdraws from a treaty in a manner that violates its own domestic law, will this withdrawal take effect in international law? The decisions to join and withdraw from treaties are both aspects of the state's treaty-making capacity. Logically, international law must therefore consider the relationship between domestic and international rules on states' treaty consent both in relation to treaty entry and exit. However, while international law provides a role for domestic legal requirements in the international validity of a state's consent when joining a treaty, it is silent on this question in relation to treaty withdrawal. Further, there has been little scholarly or judicial consideration of this question. This contribution addresses this gap. Given recent controversies concerning treaty withdrawal - including the United Kingdom's exit from the European Union, South Africa's possible withdrawal from the International Criminal Court, and the threatened US denunciation of the Paris Agreement - and the principles underlying this body of law, it is proposed that the law of treaties should be interpreted so as to develop international legal recognition for domestic rules on treaty withdrawal equivalent to that when states join treaties, such that a manifest violation of domestic law may invalidate a state's treaty withdrawal in international law.